Nathalie Kosciusko-Morizet, a flamboyant 44-year-old candidate for the Republicans party, was canvassing for votes at a Paris market on Thursday when a man called her a "stupid bobo" -- a blend of hipster and bourgeois – and shoved her leaflets in her face, causing her to fall.
The former environment minister blacked out for several minutes before being rushed to hospital.
Vincent Debraize -- mayor of Champignolles, a small village in Normandy in northern France -- denied he had verbally or physically assaulted her, Kosciusko-Morizet's lawyer Xavier Autain told AFP.
Debraize was placed in custody for "intentional violence against a person conducting public services", according to Autain.
"It is a serious attack on an elected member of the Republicans and I hope for a fitting response from the judiciary," he added.
After the attack, the man left, heading for the closest metro entrance.
He was photographed, and his picture made the rounds in French media.
French public prosecutors quickly launched an investigation.
"He was identified after witness testimony and thanks to video surveillance," said a police source.
Kosciusko-Morizet faces an uphill battle to win Sunday's second round of parliamentary elections in the well-heeled 5th, 6th and 7th districts of Paris.
Her rival, Gilles Le Gendre, a 59-year-old business consultant who represents French President Emmanuel Macron's centrist Republic on the Move party, scored 41.8 percent to her 18.1 percent in last weekend's first round.